Hero - Official game guide|
Introduction - Basics - Enemies - Maps - Secrets - Trivia
After beating the game, scroll through the levels until you see the word "BONUS!!", and press Enter. On the bonus screen, you can look at the developer maps, listen to all the music in the game, watch the ending, and play the extra level. The map of this extra level doesn't appear in the developer maps, and can only be found in this game guide.
The hidden room
A careful study of the Level 5 map on the bonus screen reveals a blinking spot in the upper left corner of the level - you can actually go through the ceiling at the end of the narrow passage in this room. In this game guide, the hidden room is clearly displayed on the map. Inside the room you'll find a strange flashing icon, forming the letters "FK" - the initials for the original name of my old webcomic Ultimortal. When you pick it up, you get a Supergun - and the icon quickly reappears, letting you pick it up again whenever you lose a life.